Such a valve may exist from the field. In particular, it may be used in connection with common-rail injection systems for diesel combustion engines. The configuration of the injector is such that it may be made up of a so-called nozzle module which may include an injection nozzle controlled by a nozzle needle, and may be activated by a so-called valve-control module having a valve-type configuration. The nozzle module may be controlled so that the nozzle module includes a valve-control space which is operatively connected to a valve-control plunger, the valve-control space also containing the fluid to be injected into the combustion chamber by the injector. A pressure change in the valve-control space effected by the valve-control module may cause a change in the position of the valve-control plunger and, thus, in the position of the nozzle needle forming a sub-assembly with the valve-control plunger as well.
As explained above, the valve-control module may have a valve-type configuration. Therefore, it may include a valve-closure member. The fluid pressure prevailing in the valve-control space of the nozzle module may act on this valve-closure member via a so-called discharge throttle. The valve-closure member may be activated by a piezoelectric actuator, which may act on the valve-closure member via a so-called control piston connected to the piezoelectric actuator, a hydraulic coupler and a so-called actuating piston connected to the valve-closure member.
When the piezoelectric actuator is activated, the valve-closure member of a valve-control module configured in this manner may be lifted off a valve seat which cooperates with it, so that the pressure prevailing in the valve-control space of the nozzle module may be reduced via the discharge throttle, thereby causing the injection nozzle to open.
A microprocessor specifying a particular control gradient may be used to activate the piezoelectric actuator. The control gradient may specify the period within which the voltage required for the expansion of the piezoelectric actuator is generated at the actuator, i.e., the period within which it obtains its maximum elongation.
A mechanical spring such as a spiral spring may prestress the piezoelectric actuator in the direction facing away from the valve-closure member. The reason for this is that the piezoelectric actuator may be unable to withstand tensile forces. In particular, such tensile forces may tear apart the individual layers of a piezoelectric actuator formed from a plurality of layers, so that short-circuits may occur and the injector may no longer be used. The magnitude of the resilience may influence only the operating point of the piezoelectric actuator, but not its lifting capacity.
In other prior injectors of the type mentioned at the outset, the compression spring may have a relatively high initial stress. However, this may require a relatively large space for the compression spring, which, in turn, may have a negative effect on the cost of the injector.